ALP — Normal Range & Interpretation

Clinical Context

Alkaline phosphatase (ALP) is an enzyme concentrated in the liver, biliary tract, bone, intestine, and placenta. Clinicians order it as part of the hepatic panel to evaluate cholestatic liver disease and as part of a bone workup to assess osteoblastic activity. Because ALP originates from multiple tissues, the clinical picture and companion labs determine its source.

Elevations point to biliary obstruction, cholestasis, primary biliary cholangitis, hepatic tumors, and infiltrative liver disease, especially when GGT rises in parallel. Bone-origin elevations occur with Paget disease, healing fractures, osteomalacia, rickets, and bone metastases. Physiologic elevations appear in pregnancy from placental ALP and in adolescents during growth spurts. Depressed ALP accompanies malnutrition, hypothyroidism, zinc or magnesium deficiency, and Wilson disease.

Board-style questions on ALP pair it with GGT to distinguish hepatobiliary from bone sources: elevated ALP with elevated GGT confirms a hepatic origin, while isolated ALP elevation with a normal GGT directs the workup toward bone. Questions frame ALP alongside bilirubin and transaminases to identify cholestatic versus hepatocellular injury patterns. Recognize pregnancy and adolescent growth as benign causes, and link markedly elevated ALP with bone pain to Paget disease. Order a fractionated ALP when the source remains unclear after initial testing.

Related Labs

• AST (SGOT) — U/L
• ALT (SGPT) — U/L
• Total Bilirubin — mg/dL
• Direct Bilirubin — mg/dL
• Albumin — g/dL

Sources

• MedlinePlus
• ARUP Consult